README.md

Temple

Temple is an abstraction and a framework for compiling templates to pure Ruby.
It's all about making it easier to experiment, implement and optimize template
languages. If you're interested in implementing your own template language, or
anything else related to the internals of a template engine: You've come to
the right place.

Have a look around, and if you're still wondering: Ask on the mailing list and
we'll try to do our best. In fact, it doesn't have to be related to Temple at
all. As long as it has something to do with template languages, we're
interested: http://groups.google.com/group/guardians-of-the-temple.

S-expression

In Temple, an Sexp is simply an array (or a subclass) where the first element
is the type and the rest are the arguments. The type must be a symbol and
it's recommended to only use strings, symbols, arrays and numbers as
arguments.

Temple uses Sexps to represent templates because it's a simple and
straightforward data structure, which can easily be written by hand and
manipulated by computers.

NOTE: SexpProcessor, a library written by Ryan Davis, includes a Sexp
class. While you can use this class (since it's a subclass of Array), it's not
what Temple mean by "Sexp".

Abstractions

The idea behind Temple is that abstractions are good, and it's better to have
too many than too few. While you should always end up with the core
abstraction, you shouldn't stress about it. Take one step at a time, and only
do one thing at every step.

So what's an abstraction? An abstraction is when you introduce a new types:

Why are abstractions so important?

First of all, it means that several template engines can share code. Instead
of having two engines which goes all the way to generating HTML, you have two
smaller engines which only compiles to the HTML abstraction together with
something that compiles the HTML abstraction to the core abstraction.

Often you also introduce abstractions because there's more than one way to do
it. There's not a single way to generate HTML. Should it be indented? If so,
with tabs or spaces? Or should it remove as much whitespace as possible?
Single or double quotes in attributes? Escape all weird UTF-8 characters?

With an abstraction you can easily introduce a completely new HTML compiler,
and whatever is below doesn't have to care about it at all. They just
continue to use the HTML abstraction. Maybe you even want to write your
compiler in another language? Sexps are easily serialized and if you don't
mind working across processes, it's not a problem at all.

All abstractions used by Temple are documented in {file:EXPRESSIONS.md EXPRESSIONS}.

Compilers

A compiler is simply an object which responds a method called #call which
takes one argument and returns a value. It's illegal for a compiler to mutate
the argument, and it should be possible to use the same instance several times
(although not by several threads at the same time).

While a compiler can be any object, you very often want to structure it as a
class. Temple then assumes the initializer takes an optional option hash:

Parsers

In Temple, a parser is also a compiler, because a compiler is just something
that takes some input and produces some output. A parser is then something
that takes a string and returns an Sexp.

It's important to remember that the parser should be dumb. No optimization,
no guesses. It should produce an Sexp that is as close to the source as
possible. You should invent your own abstraction. Maybe you even want to
separate the parsers into several parts and introduce several abstractions on
the way?

Filters

A filter is a compiler which take an Sexp and returns an Sexp. It might turn
convert it one step closer to the core-abstraction, it might create a new
abstraction, or it might just optimize in the current abstraction. Ultimately,
it's still just a compiler which takes an Sexp and returns an Sexp.

For instance, Temple ships with {Temple::Filters::DynamicInliner} and
{Temple::Filters::StaticMerger} which are general optimization filters which
works on the core abstraction.

An HTML compiler would be a filter, since it would take an Sexp in the HTML
abstraction and compile it down to the core abstraction.

Generators

A generator is a compiler which takes an Sexp and returns a string which is
valid Ruby code.

Most of the time you would just use {Temple::Generators::ArrayBuffer} or any of the
other generators in {Temple::Generators}, but nothing stops you from writing your
own.

In fact, one of the great things about Temple is that if you write a new
generator which turns out to be a lot faster then the others, it's going to
make every single engine based on Temple faster! So if you have any ideas,
please share them - it's highly appreciated.

Engines

When you have a chain of a parsers, some filters and a generator you can finally create your engine. Temple provides {Temple::Engine} which makes this very easy: